Oxidation-Induced\nLigand Swap: Oxygen Insertion into\na Cobalt-Phosphine Complex

The\nsynthesis and characterization of a half-sandwich cobalt(II)\ncomplex supported by a bidentate, pendent-amine phosphine ligand (P<sup>Ph</sup><sub>2</sub>N<sup>Bn</sup><sub>2</sub> = 1,5-diaza-3,7-diphosphacyclooctane)\nare reported. Oxidation of a cobalt(I)-phosphine precursor with silver(I)\nsalts yielded the paramagnetic complex [CpCo(P<sup>Ph</sup><sub>2</sub>N<sup>Bn</sup><sub>2</sub>)]<sup>+</sup><sub>.</sub> This species\nrapidly reacts with oxygen upon air exposure under ambient conditions,\nresulting in the insertion of oxygen into the cobalt-phosphine bonds.\nTwo cobalt complexes were generated from this reaction: the cobaltocenium\ncation, bearing two Cp ligands (Cp = cyclopentadienyl); and a cobalt(II)-bis(phosphine\noxide) dicationic complex in which two O<sub>2</sub>P<sub>2</sub>N<sub>2</sub> ligands coordinate in a <i>fac</i> fashion via\ntwo oxygen and one nitrogen centers to establish an overall octahedral\ngeometry. Thus, the aerobic oxidation of the phosphine induces the\nexchange and rearrangement of the ligands at cobalt.